Why do some umbrellas have black cover instead of silver?

Question

Or what is the use of a black cover instead of a silver one?

I have the idea that the black (only) removable cover of some umbrellas is rather an incomplete product. Is that so?

I'll try to elaborate.

A simple umbrella can be used as a reflector or as a translucent diffuser. If you need the diffuser, you remove any cover. That one is clear.

But if you need it as a reflector to bounce light, you have three options: 1) Leave the cover off 2) Use a black cover 3) Use a silver cover.

Considering that the umbrella is translucent, if you go for option 1, part of the light goes to the other side. If you are in a small room it means that some of the light will then bounce off the wall and come back to the subject. If you are outdoors or in a really big hall, there is nothing to bounce the light back so it is just lost (wasted light).

Using a cover, either black or silver will prevent light going through the umbrella. In a room it means less light hitting the walls and coming back to the subject in many directions, eliminating some "fill light" and giving a more contrasty look. But outdoors the cover won't provide that benefit.

There is where my struggle begins. My guess is that a silver cover shall bounce the light back into the umbrella, which should cause it to go through the fabric one more time and then directly to the subject, thus making a better use of the light source, while a black one will simply eat the light up. That would make the silver cover a much better choice, specially if using small flashes and shooting outdoors.

So, again, is there a reason why someone would prefer to buy an umbrella with black covers instead of the silver one?

Answer 1

I understand what you mean: you're asking about 'convertible' umbrellas that are translucent white with a removable black cover on their exterior surface. What you suggest makes sense; having a silver surface behind the white should give a theoretical improvement in their efficiency, which is important for small flashes. Perhaps it isn't done this way because using small flashes this way is a somewhat recent innovation, and bigger studio strobes simply didn't need to worry about it.

But the translucent white umbrellas shouldn't be used that way. They should be set up with the dome between the strobe and the subject, as a "shoot through" diffuser. This puts the diffusion surface closer to the subject, creating a larger light source and softer light. There will be considerable backscatter – they're open-backed softboxes, essentially – but those reflections can be used to further soften the light in the studio. Outdoors this light is usually lost (watch out for green bounce) but the benefit of having a large surface closer to the subject remains.

A reflective umbrella, with a metallic surface, provides more control over the light with less spill. This is the effect that the convertible umbrella tries to offer, but even with silver replacing the black liner it wouldn't match the efficiency of the metallic reflector as the translucent white will still create more spread and absorb more light. My solution has been to have both types on hand, silver and translucent, and use them according to what each situation requires.

Answer 2

You are confusing me here, the black part of an umbrella, if it does have one, is on the convex side, not the concave side. You remove this black cover on the convex side to shoot through the umbrella, but if you are shooting into the umbrella as a reflector - then the black will not be part of the equation and instead the material on the interior(concave) side of the umbrella is being used. That concave side is typically silver, gold, or white - I'm not familiar with this interior concave material ever being black.